Shaped abrasive

ABSTRACT

AN ABRASIVE MEMBER COMPRISING A SHELL OF SHEET OR FIBROUS MATERIAL INTIMATELY SURROUNDING A FILLER OF ABRASIVE GRAINS AND A RESILIENT BONDING AGENT, THE SHELL HAVING ONE OR MORE OPENINGS EXPOSING THE FILLER; THE SHELL MATERIAL SHOWN IS DESTRUCTIBLE WITH WEARING DOWN OF THE ABRASIVE SURFACE; SHOWN ALSO ARE THE FILLER OF POLYURETHANE FOAMS; TWISTING OR TIGHT FOLDING FOR COMPRESSING THE MATRIX PRIOR TO CURE AND TO FORM STRONG CORD LIKE ELEMENTS; WETTING OF THE SHELL FOR ADDING MOISTURE FOR THE CURE; AND ROTARY ABRASIVE MEMBERS WITH RADIAL ELEMENTS FORMED BY THIS TECHNIQUE.

United States Patent O1 ce Patented Mar. 2, 1971 3,566,551 SHAPED ABRASIVE Elisha Winthrop Hall, Jr., Greenbush, Mass., assignor to F. L. & J. C. Codman Company, Rockland, Mass. Filed Oct. 20, 1967, Ser. No. 676,895 Int. Cl. B24d 9/02, 15/ 00 U.S. Cl. 51-336 13 Claims ABSTRACT F THE DISCLOSURE An abrasive member comprising a shell of sheet or fibrous material intimately surrounding a filler of abrasive grains and a resilient bonding agent, the shell having one or more openings exposing the filler; the shell material shown is destructible with wearing down of the abrasive surface; shown also are the filler of polyurethane foams; twisting or tight folding for compressing the matrix prior to cure and to form strong cord like elements; wetting of the shell for adding moisture for the cure; and rotary abrasive members with radial elements formed by this technique.

This invention relates to abrasive members.

It is an object of this invention to provide a new abrasive member which is flexible, durable, resilient, capable of being formed into a number of desired shapes, and which has a continually self-renewing abrasive surface. Another object is to provide a new abrasive member which has the desirable characteristics of molded abrasives, including a substantial depth of abrasive and predetermined dimensional properties, and yet is capable of being easily and economically manufactured in a continuous manner without the costly and time-consuming use of molds, It is another object to provide an improved grinding or bufiing member which employs protruding elements.

'Ille invention features an abrasive member comprising a shell formed of sheet or fibrous material intimately surrounding an abrasive filler comprising abrasive grains and a resilient bonding agent, the shell having at least one opening exposing the filler. In preferred embodiments, the shell is a tube having at least one open end; the shell is of relatively flexible material which is also destructible with wearing down of the abrasive filler to provide a continuously regenerated open abrasive surface, and advantageously in certain instances the material is formed of fibers such as paper or cloth, is porous, or is heatresistant; the ller comprises a resilient bonding material, such as polyurethane foam having abrasive grains substantially uniformly dispersed throughout and bonded to it by the bonding agent; and the shell comprises a long twisted or tightly folded tube.

'Ihe invention features a rotary abrasive member comprised of a number of elements formed as above, the elements secured to a center and protruding radially exposing their sides or peripheral surfaces for abrasive action.

The invention also features a method of continuously forming an abrasive product comprising a shell of sheet or fibrous material surrounding a filler comprising abrasive grains and a resilient bonding agent, comprising the steps of providing a long strip of thin shell-forming material, spreading on the strip a strip of an abrasive mixture comprising a uniform dispersion of abrasive grains and a resilient bonding agent, conforming the shell-forming strip around the abrasive mixture to form a continuous shell compressed together with the abrasive mixture, and subjecting the abrasive mixture and shell to curing conditions to cure the resilient bonding agent.

In preferred embodiments the bonding agent is of the type requiring the presence of moisture for curing and the shell-forming material is wetted to provide the necessary moisture; the abrasive mixture includes a foamable material which foams in situ after formation of the shell, to create a compressive condition therewithin; the `filler includes a mixture of preformed foam particles and abrasive grains adhered thereto; and after the shell surrounds the filler, it is compressed more tightly by twisting, folding, or compression with rollers.

Other objects, features and advantages will appear from the following description of a preferred embodiment of the invention, taken together with the attached drawings thereof, in which:

FIG. 1 is a perspective view of a preferred embodiment of the present invention; and,

FIG. 2 is a perspective view of another preferred ernbodiment; and,

FIGS. 3a, b and c illustrate successive steps in the manufacture of a multi-folded abrasive element according to the invention;

FIG. 4 illustrates a slab form of abrasive element;

FIG. 5 illustrates a pleated slab form of abrasive element;

FIG. 6 diagrammatically illustrates abrasive members employing the abrasive elements of FIGS. 2 and 5.

FIG. 7 is a diagrammatic view of a preferred method of making an abrasive member embodying the present invention.

In FIG. l is shown an abrasive element 10 comprising a folded-over shell 12 enclosing a filler 14 containing abrasive grains 16 in a flexible bonding agent 18. In FIG. 2, the element of FIG. l has been provided with a number of twists 20 prior to curing of the bonding agent. These twists advantageously may apply pressure to the filler, stabilize the dimensions of the element, add reinforcement, and ensure a more compact and strong product.

In the embodiment shown, the shell is formed of paper. However, other fibrous material, such as cloth, woven fiberglass, etc., or plastic film such as fluro carbon film (eg. Telfon) or polyester (Mylar) may be used, depending on the strength, flexibility and work ability desired in the finished abrasive member.

Among the preferred bonding agents are the elastomeric polyurethanes (prepared, e.g. by reacting aryl diisocyanate with polyols selected from diols and high molecular weight triols). Abrasive grains 16 are preferably in the size of about 30 to 220 grit or finer, and may be of any of a number of materials (c g., silicon, carbide, aluminum oxide) having preselected cutting characteristics, to perform grinding, bufiing or polishing.

In a preferred embodiment, filler 14 also contains foam material, preferably a polyurethane foam.

In certain instances, as when the abrasive element has a small cross-section, the urethane material in nonfoamed state with abrasive grains dispersed therein is introduced to the shell, and thereafter the material foams in situ and may be cured by application of heat, moisture or catalyst through the shell, causing the material to itimately contact the shell. Preferably the foaming creates pressure which serves to limit the degree of foaming, and achieve intimate bonding of shell to filler.

In other instances, to assure a uniform dispersion of abrasive grains in foam material, abrasive grains and bonding agent are mixed with a large number of discrete pre-formed resilient urethane foam members (see copending United States Application, Hall et al., Ser. No. 456,647, filed May 18, 1965). The foam is compressed, e.g., by twisting, in the abrasive member prior to curing.

Although in the embodiments shown, the abrasive members are in the form of cord, it will be understood that many other shapes are also encompassed by the present invention. For example, a rectangular block abrasive member could be made having, e.g., a paper shell, and

then sliced to provide an exposed abrasive surface. The shell material should be so chosen that as the (preferably, a foam-containing) filler surface wears down, the surrounding shell is gradually destroyed, but without substantial tearing or flaking, to keep the remainder of the abrasive filler covered until in use. The cord itself may also be formed into squares, circles, etc., prior to curing, cured to retain the orientation, and then cut to provide an abrasive surface.

FIG. 3a shows a folded embodiment in its first stage of manufacture. The shell-forming sheet material 12 is provided in strip form, and a strip of abrasive filler 14 is applied to it. Referring to FIGS. 3b and 3c, the sheet is successively folded, compressing the filler and shell forming material together. As suggested by the arrows in FIG. 3c, further compression eg. by a pair of rollers is possible, but in many instances the Ilinal folding operation itself, will sufliciently compress the shell and filler.

In the embodiment of FIGS. 1 3, the twisting and folding pressure may be maintained by the machine until the cure is completed, or the product may be wound upon a spool to maintain compression during cure, or the shell may itself be glued or receive a permanent set to maintain compression until the filler cures.

Referring to FIG. 4 a wrapped slab is shown which can be formed according to the invention. For such an embodiment pressure surfaces, e.g. liat 'belts urged together, may maintain compression upon the shell until cure is completed.

In FIG. 5 it is shown that the slab 20 can be pleated and in FIG. 6 a number of slabs 20 are shown radially protruding from a hub 22 to which they are joined to define a rotatable working surface. The sides of the slabs may be exposed to provide a face disc, as suggested in area 24, or the ends 26 of the slab are exposed to provide a peripheral working surface, in form much like that of a known type of polishing buff, but because of the ability to use Various filler hardnesses and grit size, the abrasive member can be'employed for rigorous grinding purposes, etc.

FIG. 6 also illustrates the twisted cord element 10 of FIG. 1 radially secured to hub 28 in the form of a known finger buff. Again a wide range of abrasive and grinding action can be obtained.

In FIG. 7, abrasive cord is made continuously by feeding a strip 30 of fibrous material from roll 32, over wetting rollers 33, and past hopper 34, where a strip of abrasive mixture is applied through spreader 36. The strip passes first into stationary chuck rolls 38 into rotating chuck assembly 40 by which the strip is folded around the abrasive mixture, and twisted, rollers 38 preventing the twist from proceeding any further back toward hopper 34.

The twisted cord is compressed between roller nip 42,

cured in oven 44, and rolled up onto reel 46, the axis turning as shown.

Other embodiments will be obvious to those skilled in the art and are within the following claims.

What is claimed is:

1. An abrasive element comprising an abrasive filler and a thin shell substantially enclosing said filler,

said abrasive filler comprising abrasive grains and resilient compressed body-forming foam material, said 4 grains dispersed in said foam material, and said shell having at least one opening exposing said abrasive filler, and formed of material that is destructible with wearing down of said abrasive filler.

2. The abrasive element of claim 1 wherein said shell is of tubular form.

3. The abrasive element of claim 2 wherein said opening is at the end of said tubular shell.

4. The abrasive element of claim 1 wherein said shell is of relatively flexible sheet form material.

5. The element of claim 1 lwherein said shell is made of paper.

6. The element of claim 1 wherein said abrasive filler comprises resilient body-forming foam material having abrasive grains substantially uniformly dispersed therein.

7. The abrasive element of claim 1 wherein said foam material comprises a large number of discrete, pre-formed polyurethane foam body particles compressively bonded to each other and to said abrasive grains by said resilient bonding agent.

8. The abrasive element of claim 7 wherein said bodyforming material is polyurethane foam.

9. The abrasive element of claim 1 wherein said shell comprises a long narrow tube having a series of helical twists therein.

10. An abrasive member comprising a plurality of abrasive elements each comprising an abrasive filler and a thin shell substantially enclosing said filler, said abrasive liller comprising abrasive grains and resilient compressed body-forming foam material, said grains dispersed in said foam material, and said shell having at least one opening exposing said abrasive filler, and formed of material that is destructible with wearing down of said abrasive liller, said elements being radially disposed about and secured to a hub, and said openings of said elements exposing said filler disposed to define a rotatable working surface.

11. The abrasive member of claim 10 wherein the ends of said radial elements define a peripheray working surface.

12. The abrasive element of claim 1 wherein said abrasive liller includes a resilient bonding agent bonding said grains and said compressed foam and cured with said foam in a compressed state,

and said shell is constructed to enclose a volume less than the volume occupied by said foam in its uncompressed state, said shell exerting compressive forces on said foam.

13. The abrasive element of claim l2 wherein said shell encloses a volume in the shape of a helical twist formed by twisting a tubular-shaped shell about its longitudinal axis.

References Cited UNITED STATES PATENTS 3,256,075 6/1966 Kirk 5 1-298X 2,122,665 7/1938 Twyning 51-263 2,861,401 1l/l958 Peterson 51-337 1,692,329 11/1928 Burlew 5l-298UX HAROLD D. WHITEHEAD, Primary Examiner U.S. C1. X.R. 51-394 

